1. Field of the Invention
This invention relates to an electronic camera which stores, in storage medium, digital data corresponding to an object image.
2. Description of the Prior Art
Recently, with the rapid development of semiconductor technology, small semiconductor memories having large capacities are available at comparatively low costs. Also, in the field of video equipment for home and personal use, video tape recorders (VTR) having a memory capable of storing color TV signals for one frame (hereinafter referred to as "frame memory") have been developed as manufactured articles. A type of electronic still video camera has also been made public which has a detachable memory pack incorporating a memory capable of storing color image signals for several tens of frames, and in which color video signals for one field or one frame corresponding to a still image taken by the camera are stored in the memory of the memory pack.
To increase the number of frames stored in this kind of electronic camera without increasing the size of the memory pack, it is necessary to reduce the number of data items for one frame. If the number of data items is reduced simply by reducing the number of samples, the image quality is deteriorated. It is therefore desirable to reduce the number of data items by high efficiency encoding techniques well known in the field of digital signal processing.
In a case where color video signals are digitized, however, the data rate is extremely high. For example, in a case where a frame having 500.times.700 pixels is digitized and where a luminance signal and two color difference signals are sampled respectively by 8 bits, the total number of data items is (500.times.700.times.3.times.8=) 8.4 Mbits. If this large amount of data is transmitted within 1/30 sec. according to the frame frequency, the data rate is 252 Mbps and thus extremely high.
It is not possible to design an encoding circuit for high efficiency encoding of a data sequence of such a large data rate even if high speed circuit elements are utilized. Ordinarily, for such encoding, a plurality of encoding circuits are used to effect parallel processing to reduce the necessary processing speed of each encoding circuit.
For encoding based on parallel processing, a plurality of high efficiency encoding circuits must be provided for processing each of the two color difference signals, and the scale of hardware is thereby increased. Also, circuit elements having maximized processing speeds are required for the encoding circuits. Under these conditions, it is difficult to reduce the total cost of the camera.